As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand of secondary batteries has also sharply increased. One of the secondary batteries is a lithium secondary battery having high energy density, high operation voltage, and excellent storage and service life characteristics, which is now widely used as an energy source for various electronic products as well as various kinds of mobile devices.
However, various combustible materials are contained in the lithium secondary battery. As a result, there is a possibility of danger in that the lithium secondary battery can be heated or explode due to overcharge, overcurrent, or any other external physical impacts. In other words, the lithium secondary battery has low safety. Consequently, a protection circuit module (PCM) for effectively controlling the abnormality of the battery, such as overcharge, is mounted in the lithium secondary battery while the PCM is connected to a battery cell of the lithium secondary battery.
The PCM includes a field effect transistor (FET), which serves as a switching element for controlling electric current, a voltage detector, and passive elements such as a resistor and a capacitor. The PCM interrupts overcharge, overdischarge, overcurrent, short circuits, and reverse voltage of the battery to prevent the explosion or the overheating of the battery, the leakage of liquid from the battery, and the degradation of the charge and discharge characteristics of the battery, and to suppress the lowering of the electrical efficiency of the battery and the abnormal physicochemical behavior of the battery, thereby eliminating dangerous factors from the battery and increasing the service life of the battery.
Generally, the PCM is connected to the battery cell using a conductive material, such as a plate, by welding or soldering, which increases a coupling force between the PCM and the battery cell. However, the welding or soldering process requires a high degree of technical skill with the result that skilled persons are needed. Also, the welding or soldering process requires large working space. Furthermore, when physical impacts are applied to the battery cell, electrical shorts may occur, and therefore, the battery cell may catch fire or explode. In other words, safety-related problems may occur.
Consequently, research on various no-welding type technologies, which can complement drawbacks of the welding or soldering process while maintaining advantages of the welding or soldering process, is being rapidly pursued. For example, Korean Unexamined Patent Publication No. 2004-0015314 discloses a structure for mounting a protection circuit to a battery cell wherein a printed circuit board, which includes a protection circuit part and a protruding contact pact, is coupled to a fixing part, which is formed by injection molding of plastic, through the coupling between the protruding contact pact and the fixing part, and then the fixing part is mounted to the battery cell. Also, Korean Unexamined Patent Publication No. 2005-0074197 discloses a structure for mounting a protection circuit to a battery cell wherein a component part, which surrounds a circuit board and has a coupling-type protrusion formed at the outer surface thereof, the protrusion being provided with a jaw, is manufactured by molding, and the component part is connected to the battery cell using the protrusion. Furthermore, Korean Unexamined Patent Publication No. 2004-0062914 discloses a structure for mounting a protection circuit to a battery cell wherein a hook is formed at the lower end case of a battery such that a terminal can be coupled to an electrode part in a hook fashion, grooves are formed at the terminals, and the protection circuit is assembled to the terminal in a hook fashion.
According to the above-described methods, additional members, which include the protection circuit, are connected to the battery cell in a coupling fashion without using the conventional welding process, whereby the problems caused from the conventional welding process are solved. However, the above-described methods are not suitable for a battery cell including various kinds of electrode terminals, such as plate-shaped electrode terminals. In addition, since the connection between the additional members including the protection circuit and the battery cell is accomplished merely in an inserting and coupling fashion, the coupling force between the additional members including the protection circuit and the battery cell is low, and therefore, a possibility that the additional members including the protection circuit is separated from the battery cell is high. Furthermore, the protection circuit and the electrode terminals are electrically connected with each other merely through the contact between the protection circuit and the electrode terminals, and therefore, the connecting force between the protection circuit and the electrode terminals is also low.